The National Rifle Association is on the offensive this political season, with an effort to defeat President Obama. It's also been in damage control mode, fending off calls for tighter gun laws following the massacre in a Colorado theater.

In a more unusual move, the NRA is also trying to unseat one of its own, a Republican state legislator in Tennessee.

Blake Farmer of member station WPLN in Nashville explains.

BLAKE FARMER, BYLINE: It's good, old-fashioned payback. The head of the NRA's lobbying arm, Chris Cox, has taken a personal interest in a Republican primary, appearing in this Web video.

(SOUNDBITE OF WEB VIDEO)

FARMER: State representative Debra Maggart of Hendersonville, Tennessee crossed the NRA by helping block an effort to allow people to keep guns in their vehicles at work. She says it would have trampled on private property rights of business owners. The NRA's wrath is trained on this ranking Republican incumbent, but gun owners are irritated with the state's GOP leadership as a whole. Maggart just went along with the Republican governor, who had been told in no uncertain terms by the state's largest employers they wanted the guns-in-trunks bill scuttled.

UNIDENTIFIED MAN: Mr. Cox?

: I'm Chris, yes.

FARMER: I ran into the NRA's chief lobbyist at the Tennessee GOP's annual statesman dinner. Everyone at this soiree supposedly plays on the same team, but the NRA has made the family get-together a little uncomfortable this year. I caught this chance encounter while talking to Cox.

UNIDENTIFIED MAN: This is your best friend, Debra Maggart.

: Representative.

(LAUGHTER)

STATE REPRESENTATIVE DEBRA MAGGART: Take a picture, quick. Oh, he's a radio guy. That won't work. Good to see you.

: You, too. Take care.

FARMER: Beneath the veneer of pleasantries, Cox is making an example of Maggart, so other Republicans think twice before stepping out of line. This year, the NRA has also endorsed the challenger in seven Republican primaries in Kansas, and one in Georgia. But in Tennessee, it's an outright media campaign to defeat this GOP incumbent. At the end of June, the NRA had already spent $75,000 - unheard of in a contest like this. Cox says the independent expenditure is justified.

: It's our First Amendment right to assemble, to petition our government. That's what we're doing.

MAGGART: You know, they've got to have a reason to collect your dues. You know, they've got to have a reason for people to send them a check.

FARMER: Maggart, herself a member, has been sending the NRA checks for years, and contends she's about as big a gun gal as she could be. She hosts a skeet shoot fundraiser. She has her carry permit, and is a regular at the local indoor shooting range, which has turned its back on her.

(SOUNDBITE OF GUNFIRE)

FARMER: Would-be voters take target practice with 45-caliber pistols. What's in the window says it all: signs for Maggart's opponent, political newcomer Courtney Rogers. The retired Air Force officer says she's even surprised at some of the NRA's tactics, like plastering Maggart's face on those billboards beside President Obama.

COURTNEY ROGERS: I didn't even know what to say. I just looked at it and I said: She's not going to like that.

(LAUGHTER)

FARMER: Still, Rogers welcomes the NRA in her corner. And the outside spending may be paying off.

JIM FITZGERALD: Yeah, what can I do for you?

ROGERS: Good morning, Mr. Fitzgerald.

FITZGERALD: Hello.

ROGERS: My name's Courtney Rogers.

FITZGERALD: I know. I recognize you, and I'm voting for you.

FARMER: Campaigning door to door, Rogers gets a warm reception from Jim Fitzgerald, a gun owner who calls Maggart wishy-washy on the weapons issue. But there are signs the NRA is turning off voters, too. Bill Taylor voted early, and says he supported a friend.

BILL TAYLOR: Debra Maggart's a lifetime NRA member, as I am, as a lot of all of us are, and we may drop our membership because of that.

FARMER: Taylor said the NRA trying to take out one of its own is inappropriate and irresponsible. He also worries the campaign may be effective. For NPR News, I'm Blake Farmer, in Nashville.